One of the central problems in neurobiology is the detailed working out of the ways in which organized systems of neurons accomplish their functions of representing, modifying, and transmitting information while controlling the activities of the organism. We propose to study the organizational principles of neural systems: how the anatomical and physiological properties of the constituent cells combine to comprise a working system. Previous work has shown that statistical investigation of the temporal relationships among nerve impulses can reveal otherwise hidden relationships among the corresponding neurons and can furnish the basis for elucidating neural coding schemes. The investigations in this project carry this work forward, in several directions: (1) Mathematical and theoretical studies of principles of interaction in neuronal populations. (2) Development and extension of statistical techniques for the analysis and interpretation of experimentally observed nerve-impulse activity in specific preparations. (3) Development and extension of digital computer programs for simulating the behavior of specific neural networks and for practical application of the statistical techniques by the experimental neurophysiologist. (4) Application of theory, statistical techniques, and simulation to specific neural systems, in conjunction with experimental investigations supported separately, including ganglion cells in Aplysia, interneurons in crayfish and lobster, frog cerebellar cortex, vertebrate retina, and branching nerve fibers in tissue culture.